Motion Of Coronal Mass Ejections Research Articles

CME Velocity Field Calculation Model Based on an Unsupervised Transformer Optical Flow Network

The optical flow algorithm (OF) is one the main methods for calculating image velocity field and has many applications in space weather. Most OF calculations are applied to the motion of labeled rigid objects and are not suitable for velocity detection of high-energy particles, such as in a coronal mass ejection (CME). Fluctuations in exposure time and the influence of space weather will lead to inconsistent brightness of the same feature point at different times. To address this problem, we propose an unsupervised multiscale optical flow network based on Vision Transformer, named UTFlowNet. The network comprises a multiscale feature extraction module and a coarse-to-fine global optical flow calculation module. The movement of high-energy particles emitted during a CME eruption follows certain physical rules. Therefore, we apply fluid motion–based loss functions to analyze the motion of high-energy particles more effectively, addressing the problem of CME motion field extraction. Our method can be applied to the real-time automatic extraction of a CME’s velocity field and performs well with inconsistent brightness, large-scale motion, and strong CME noise. Additionally, we can estimate subpixel level fine-grained velocity. Our model may be affected by overfitting during cross–data set inference, so we encourage performing a small amount of transfer learning on new data sets to mitigate this issue. In order to verify the accuracy of our method, we conducted experiments and verification on the Solar and Heliospheric Observatory LASCO C2 data and the High Altitude Observatory MLSO data. We constructed a large-scale displacement simulation data set based on LASCO C2 data and tested on it, achieving the best results.

Kinematic characteristics of stealth CME in three-dimensional space

We have studied and compared kinematic characteristics of the motion of coronal mass ejections (CMEs) in three-dimensional (3D) space for three groups of CMEs for the period 2008–2014. These CME groups include: (i) stealth CMEs, (ii) CMEs that originate on the front side of the Sun (for an observer on Earth) and are associated with X-ray flares and filament eruption, (iii) all CMEs registered during the given period. Stealth CMEs are CMEs that emerge on the front side of the Sun and are unrelated to X-ray flares, as well as to filament eruption. We compare kinematic and some physical characteristics of these CMEs with those of a separate group of CMEs, classified as stealth in [D’Huys et al., 2014]. After comparing the characteristics of the three CME groups (i)–(iii), we concluded that stealth CMEs have, on average, the lowest velocity, kinetic energy, mass and angular size, central position angle, and also the angle φ between the direction of CME motion in the ecliptic plane and the Sun–Earth line and the angle λ between the direction of CME motion in 3D space and the ecliptic plane. We also discuss distributions of CMEs of different types by kinematic characteristics.

Кинематические характеристики КВМ типа stealth в трехмерном пространстве

We have studied and compared kinematic characteristics of the motion of coronal mass ejections (CMEs) in three-dimensional (3D) space for three groups of CMEs for the period 2008–2014. These CME groups include: (i) stealth CMEs, (ii) CMEs that originate on the front side of the Sun (for an observer on Earth) and are associated with X-ray flares and filament eruption, (iii) all CMEs registered during the given period. Stealth CMEs are CMEs that emerge on the front side of the Sun and are unrelated to X-ray flares, as well as to filament eruption. We compare kinematic and some physical characteristics of these CMEs with those of a separate group of CMEs, classified as stealth in [D’Huys et al., 2014]. After comparing the characteristics of the three CME groups (i)–(iii), we concluded that stealth CMEs have, on average, the lowest velocity, kinetic energy, mass and angular size, central position angle, and also the angle φ between the direction of CME motion in the ecliptic plane and the Sun–Earth line and the angle λ between the direction of CME motion in 3D space and the ecliptic plane. We also discuss distributions of CMEs of different types by kinematic characteristics.

Solar Energetic Particle Acceleration by a Shock Wave Accompanying a Coronal Mass Ejection in the Solar Atmosphere

Abstract Solar energetic particle acceleration by a shock wave accompanying a coronal mass ejection (CME) is studied. The description of the accelerated particle spectrum evolution is based on the numerical calculation of the diffusive transport equation with a set of realistic parameters. The relation between the CME and shock speeds, which depend on the initial CME radius, is determined. Depending on the initial CME radius, its speed, and the magnetic energy of the scattering Alfvén waves, the accelerated particle spectrum is established 10–60 minutes from the beginning of CME motion. The maximum energies of particles reach 0.1–10 GeV. The CME radii of 3–5 and the shock radii of 5–10 agree with observations. The calculated particle spectra agree with the observed ones in events registered by ground-based detectors if the turbulence spectrum in the solar corona significantly differs from the Kolmogorov one.

Characteristics of the motion of coronal mass ejections and related shocks depending on the heliocentric distance

The 3D characteristics of the coronal mass ejection (CME) body and shock at different distances (R) from the Sun’s center have been determined for several fast halo CMEs based on data from the Large Angle and Spectrometric Coronagraph Experiment (LASCO): the positions of the CME body boundary and the related shock on their axes, the directions and velocities of these points, the distance between a shock and the CME body boundary ΔR(R), and the difference between the velocities of these structures ΔV(R) and their angular dimensions. It was shown that the character of variations in the positions and velocities of the CME body boundary and a shock differs at different distances. The dependences of parameter [ΔR/Rcme](R), where Rcme is the curvature radius of the CME body boundary on the CME axis, were constructed. The obtained dependence was compared with the ΔR/Rcme (MA(R)) dependence. Here MA is the Alfven Mach number. The relation of ΔR/Rcme to MA was obtained by Russell and Mulligan (2002) for shocks in the Earth’s orbit. A comparison of [ΔR/Rcme](R) performed in two ways makes it possible to conclude that shocks related to a CME body are piston-like, with the CME body as a piston, at least at a distance of R > 10R0 (R0 is the solar radius).

THE FIRST GROUND LEVEL ENHANCEMENT EVENT OF SOLAR CYCLE 24: DIRECT OBSERVATION OF SHOCK FORMATION AND PARTICLE RELEASE HEIGHTS

We report on the 2012 May 17 Ground Level Enhancement (GLE) event, which is the first of its kind in Solar Cycle 24. This is the first GLE event to be fully observed close to the surface by the Solar Terrestrial Relations Observatory (STEREO) mission. We determine the coronal mass ejection (CME) height at the start of the associated metric type II radio burst (i.e., shock formation height) as 1.38 Rs (from the Sun center). The CME height at the time of GLE particle release was directly measured from a STEREO image as 2.32 Rs, which agrees well with the estimation from CME kinematics. These heights are consistent with those obtained for cycle-23 GLEs using back-extrapolation. By contrasting the 2012 May 17 GLE with six other non-GLE eruptions from well-connected regions with similar or larger flare size and CME speed, we find that the latitudinal distance from the ecliptic is rather large for the non-GLE events due to a combination of non-radial CME motion and unfavorable solar B0 angle, making the connectivity to Earth poorer. We also find that the coronal environment may play a role in deciding the shock strength.

DISTURBED ZONE AND PISTON SHOCK AHEAD OF CORONAL MASS EJECTION

The 2010 June 13 coronal mass ejection (CME) propagating toward the position angle P.A. Almost-Equal-To 245 Degree-Sign (measured counterclockwise from the Sun's north pole) was studied from the SDO/AIA and SOHO/LASCO C2, C3 data. We show that ahead of the CME frontal structure, as a result of its interaction with the undisturbed solar wind, a disturbed region (with an increased and disturbed plasma density), whose size increases as the CME travels away from the Sun, emerges gradually. Discontinuity formation at the disturbed zone front is observed in the narrow P.A. Almost-Equal-To 245 Degree-Sign -250 Degree-Sign range. Its characteristics satisfy the properties of a piston collision shock. In the other directions relative to the CME motion axis (P.A. > 250 Degree-Sign and P.A. V{sub A} (R), where u(R) is a CME velocity relative to the surrounding solar wind and V{sub A} (R) is a local Alfven velocity that is approximately equal to the velocity of fast magnetic sound in the solar corona. (2) At R 10-15 R{sub Sun }, one observes the formation of a new discontinuity {delta}{sup *}{sub F} << {lambda}{sub p} wide at the head of the collision front. Within limits of error, {delta}{sup *}{sub F} does not depend on R and is determined to be {delta}{sup *}{sub F} Almost-Equal-To 0.1-0.2 R{sub Sun} by the LASCO C3 spatial resolution and {delta}{sup *}{sub F} Almost-Equal-To 0.03 R{sub Sun} for COR2. This discontinuity is identified with a collisionless shock.« less

An Analytical Model to Predict the Arrival Time of Interplanetary CMEs

Referring to the aerodynamic drag force, we present an analytical model to predict the arrival time of coronal mass ejections (CMEs). All related calculations are based on the expression for the deceleration of fast CMEs in the interplanetary medium (ICMEs), ˙ v =− 1 15 700 (v − VSW) 2 ,w hereV SW is the solar wind speed. The results can reproduce well the observations of three typical parameters: the initial speed of the CME, the speed of the ICME at 1 AU and the transit time. Our simple model reveals that the drag acceleration should be really the essential feature of the interplanetary motion of CMEs, as suggested by Vrsnak and Gopalswamy (J. Geophys. Res. 107, 1019, 2002).

QUASI-PERIODIC OSCILLATIONS IN LASCO CORONAL MASS EJECTION SPEEDS

Quasi-periodic oscillations in the speed profile of coronal mass ejections (CMEs) in the radial distance range 2-30 solar radii are studied. We considered the height-time data of the 307 CMEs recorded by the Large Angle and Spectrometric Coronagraph (LASCO) during 2005 January-March. In order to study the speed-distance profile of the CMEs, we have used only 116 events for which there are at least 10 height-time measurements made in the LASCO field of view. The instantaneous CME speed is estimated using a pair of height-time data points, providing the speed-distance profile. We found quasi-periodic patterns in at least 15 speed-distance profiles, where the speed amplitudes are larger than the speed errors. For these events we have determined the speed amplitude and period of oscillations. The periods of quasi-periodic oscillations are found in the range 48-240 minutes, tending to increase with height. The oscillations have similar properties as those reported by Krall et al., who interpreted them in terms of the flux-rope model. The nature of forces responsible for the motion of CMEs and their oscillations are discussed.

Hybrid Reconstruction to Derive 3D Height – Time Evolution for Coronal Mass Ejections

We present a hybrid combination of forward and inverse reconstruction methods using multiple observations of a coronal mass ejection (CME) to derive the 3D 'true' Height-Time plots for individual CME components. We apply this hybrid method to the components of the 31 Dec 2007 CME. This CME, observed clearly in both the STEREO A and STEREO B COR2 white light coronagraphs, evolves asymmetrically across the 15 solar radius field of view with in a span of three hours. The method has two reconstruction steps. We fit a boundary envelope for the potential 3D CME shape using a flux rope-type model oriented to best match the observations. Using this forward model as a constraining envelope, we then run an inverse reconstruction solving for the simplest underlying 3D electron density distribution that can, when rendered, reproduce the observed coronagraph data frames. We produce plots for each segment to establish the 3D or "true" Height-Time plots for each center of mass as well as for the bulk CME motion, and use these plots along with our derived density profiles to estimate the CME asymmetric expansion rate.

Kinematics of coronal mass ejections between 2 and 30 solar radii

Kinematics of more than 5000 coronal mass ejections (CMEs) measured in the distance range 2-30 solar radii is investigated. A distinct anticorrelation between the acceleration, a, and the velocity, v, is found. In the linear form, it can be represented as a = -k 1 (v - v 0 ), where v 0 = 400 km s -1 , i.e., most of CMEs faster than 400 km s -1 decelerate, whereas slower ones generally accelerate. After grouping CMEs into the width and mean-distance bins, it was found that the slope k 1 depends on these two parameters: k 1 is smaller for CMEs of larger width and mean-distance. Furthermore, the obtained CME subsets show distinct quadratic-form correlations, of the form a = -k 2 (v - v 0 )|v - v 0 |. The value of k 2 decreases with increasing distance and width, whereas v 0 increases with the distance and is systematically larger than the slow solar wind speed by 100-200 km s -1 . The acceleration-velocity relationship is interpreted as a consequence of the aerodynamic drag. The excess of v 0 over the solar wind speed is explained assuming that in a certain fraction of events the propelling force is still acting in the considered distance range. In most events the inferred propelling force acceleration at 10 solar radii ranges between a L = 0 and 10 m s -2 , being on average smaller at larger distances. However, there are also events that show a L > 50 m s -2 , as well as events indicating a L < 0. Implications for the interplanetary motion of CMEs are discussed, emphasizing the prediction of the 1 a.u. arrival time.

On the dynamics and structure of coronal mass ejections

This paper investigates a number of general properties of loop-shaped coronal mass ejections (CMEs). It is shown that at distances 2.5 R⊙ ⩽ R ⩽ 10 R⊙ from the Sun's center the motion of CME in the plane of sky can be visualized as the radial motion of a quasi-circular region in the antisunward direction with the velocity of the center of gravity ≈ ( V p − V ⊥) and a simultaneous expansion with respect to this center with velocity V ⊥, with the quasi-circular shape remaining unchanged. At a certain distance r > 2.5 R⊙ the relationship V ⊥ V gr − V ⊥≈ const begins to be saturated. Using an improved variant of Webb's (1988) ( J. geophys. Res. 93, 1749) model it is shown that, according to its structure, the CME can be shaped both as a loop and as a shell and as a filled shell. With the obtained properties allowed for, we have calculated the velocity V r of the CME's forefront, its mass and total kinetic energy E for cases where the motion of the CME occurs at an angle β to the plane of sky.